(a) Field of the Invention
This invention relates to an illuminating optical system for high magnification endoscopes.
(b) Description of the Prior Art
In an endoscope of a high magnification, the object point is so close and the range to be observed is so small that, in order to secure a flat illumination, the optical axis of the illuminating optical system and the optical axis of the observing optical system must coincide with each other or must intersect each other at an object point.
FIG. 1 shows an endoscope illuminating optical system mentioned in Japanese utility model laid-open No. 14276/1975 as an example in which the optical axis of the illuminating optical system and the optical axis of the observing optical system are made to coincide with each other. In the case of this example, in the observing optical system, the light starting from the object point P will pass through the cover glass 1, the stop 3 provided in the reflecting plate 2 and the objective lens 4 to form an image at the end of the image guide 5. On the other hand, in the illuminating optical system, the reflecting plate 2 is inclined by 45 degrees to the optical axis of the observing optical system so that the light emitted from the exit end of the light guide 6 will have its optical axis coincided with the optical axis of the observing optical system and will pass through the cover glass 1 to illuminate the object point P. The illuminated range A can well cover the observed range B. However, in this example, there have been problems that the distance from the exit end of the light guide 6 to the object point P is so long that no sufficient illuminating light amount can be obtained and, as the flare light generated on the surface of the cover glass 1 is to be seen directly in the observing system, no clear image can be obtained.
FIG. 2 shows an endoscope illuminating optical system mentioned in Japanese patent publication No. 12107/1968 as another example in which the optical axis of the illuminating optical system and the optical axis of the observing optical system are made to coincide with each other. In the case of this example, in the observing optical system, the eyepiece 7 is arranged in the rear of the rear end of the curved image guide 5 so that the light starting from the object M will enter the front end of the image guide 5 through the objective lens 4, will pass through the image guide 5 and will come out of its rear end to be observed through the eyepiece 7. On the other hand, in the illuminating optical system, the adaptor 8 of the same material as of the glass coating fibers of the image guide 5 is provided in the bent part 5a of the image guide 5 so that the light starting from the light source 9 will pass through the condenser lens 10, will enter the bent part 5a through the adaptor 8, will have its optical axis coincided with the optical axis of the observing optical system when the light comes out of the front end of the image guide 5 and will pass through the objective lens 4 to illuminate the object M. In this example, there have been problems that, as the distance from the front end of the image guide 5 to the object M is comparatively shorter and the objective lens 4 is located between them, the light amount can be secured by adjusting the light source 9 but the flare light occurred on the surface of the objective lens 4 is to be seen directly in the observing system and no clear image can be obtained. Also, it has not been practical as a form to arrange such illuminating system in the course of the image guide 5.
FIG. 3 shows an endoscope illuminating optical system mentioned in Japanese patent laid-open No. 10033/1983 as an example in which the optical axis of the illuminating optical system and the optical axis of the observing optical system are intersected with each other. In the case of this example, the cover glass 1 has a reflecting surface 1a located in front of the light guide 6, an objective lens side surface 1b intersecting rectangularly with the optical axis of the objective lens 4 and facing the objective lens 4 and an object side surface 1c parallel with said surface 1b and exposed to the front face of the tip part of the endscope so that the illuminating light emitted from the light guide 6 will be reflected by the reflecting surface 1a, will be then totally reflected by the objective lens side surface 1b and will intersect that optical axis (of the observing optical system) of the objective lens 4 on the object side surface 1c. If the medium in contact with the object side surface 1c of the cover glass 1 is air, the light will not permeate out but, in case the tip part of the endoscope is adjacent close to the object, the medium in contact with the object side surface 1c will be water, for example, within a human body and therefore a light will be passed through the object side surface 1c. Therefore, in this example, there is the advantage that the flare lights produced on the surfaces of the cover glass 1 and the objective lens 4 do not enter into the observation range. However, there have been the problems that, as the illuminating light is reflected twice before it reaches the object point, the light path length becomes greater, and the loss of light by Fresnel's reflection amounts to about 16%, so that the amount of light becomes insufficient.
This and other objects of the present invention will become more apparent during the course of the following detailed description and appended claims.